muelectrode studies in cultured epithelial cells

The present analysis was done to elucidate the electrical properties of an established mammalian epithelial cell line, i.e. the Madin Darby canine kidney (MDCK) cell. Rapid changes of the extracellular fluid were made to identify conductive pathways across the cell membrane. During control conditions mimicking in vivo extracellular fluid, the potential difference across the cell membrane (Um) approached −51.0±0.5 mV (n = 122). With potassium-sensitive muelectrodes, a potential difference of +14,4 ± 1.4 mV (n = 5) was determined. Rapid increase of the extracellular potassium concentration from 5.4 to 20 mmol/dm3 depolarized Um (dUmK) by +17.0 ± 0.4 mV (n = 85). Accordingly, some 50% of the cell membrane conductance is due to potassium conductive pathways, i.e. the transference number for potassium (tK) approaches 0.5. When 10 μmol/dm3 valinomycin was added to the extracellular fluid, Um increased gradually to −74.7 ± 0.8 mV and tK increased to 0.86. Barium at a concentration of 1 mmol/dm3 in the extracellular fluid depolarized Um by +20.2 ± 0.4 mV and virtually abolished tK. However, when extracellular potassium was increased from 5.4 to 35 mmol/dm3, further depolarization was observed, indicating that barium can be displaced by high potassium concentrations. Rapid reduction of the extracellular sodium concentration from 133 to 19 mmol/dm3 led to a significant sustained hyperpolarization (dUmNa) of −13.5±0.6 mV (n =15). Additional experiments indicated that the hyperpolarization was at least partly due to opening of potassium conductive pathways.